Precommercial thinning in Pseudotsuga, Tsuga, and Abies stands affected by armillaria root disease: 10-year results.

Four 10- to 20-year-old stands were precommercially thinned to determine the effects of thinning on tree growth and mortality caused by armillaria root disease in the Cascade Range of western Oregon and Washington, U.S.A.: one stand of Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco var. menziesii) and noble fir (Abiesprocera Rehd.), one of Douglas-fir and western hemlock (Tsugaheterophylla (Raf.) Sarg.), one of Douglas-fir alone, and one of Shasta red fir (AbiesmagnificaA. Mutt. var. shastensis Lemm.) and mountain hemlock (Tsugamertensiana (Bong.) Carr.). After 10 years, differences in crop-tree mortality between thinned and unthinned plots were not significant in any of the four stands. Tree radial growth was significantly increased by thinning in 6 of 15 plots. Crop-tree basal area (per hectare) growth was significantly greater in thinned plots. Basal area (per hectare) growth of all trees was significantly greater in unthinned plots. Apparently, from a root-disease perspective, precommercial thinning...